1. Field of the Invention
The present invention relates to a method of fabricating an organic light emitting display and, more particularly, to a donor substrate for a laser induced thermal imaging method capable of controlling static electricity and a method of fabricating an organic light emitting display using the same.
2. Description of the Related Art
Recently, since an organic light emitting display (OLED) has low voltage driving characteristics, high luminous efficiency, wide viewing angle and rapid response speed to display a high quality moving picture, the OLED is attracting public attention as a next generation flat panel display.
In addition, the OLED is constituted of an organic layer including an organic emission layer disposed between an anode and a cathode. Since the OLED is an emissive display capable of emitting light due to recombination of electrons and holes in the organic emission layer by applying voltage to the two electrodes, the OLED does not require a backlight unit, unlike a liquid crystal display (LCD). Therefore, it is possible to make the OLED in a lightweight and thin type, and using simple processes.
The OLED is classified into a small molecular OLED and a polymer OLED according to the material of the organic layer, in particular, the organic emission layer.
The small molecular OLED includes multiple organic layers having different functions from each other, which are interposed between an anode and a cathode, wherein the multiple organic layers include a hole injection layer, a hole transport layer, an emission layer, a hole blocking layer and an electron injection layer. These layers may be adjusted by doping to prevent the accumulation of electric charges or replacing with a material having a suitable energy level. The small molecular OLED is generally made by a vacuum deposition method and thus it is difficult to realize a large-sized display.
On the other hand, the polymer OLED has a single layer structure having an organic emission layer interposed between an anode and a cathode or a double layer structure including a hole transport layer in addition to the organic emission layer, and thus may be fabricated into a thin device. In addition, since the organic layer is formed by a wet coating method, the polymer OLED may be fabricated under atmospheric pressure, thereby reducing the manufacturing cost and readily realizing the large-sized OLED.
In the case of a monochrome device, the polymer OLED may be simply fabricated by a spin coating method, but has disadvantages of lower efficiency and shorter lifetime compared to the small molecular OLED. In the case of a full color device, emission layers for showing three primary colors of red, green and blue may be patterned in such an OLED to realize the full color. In this case, the organic layer of the low small OLED may be patterned by a shadow mask deposition method, and the organic layer of the polymer OLED may be patterned by an ink jet printing method or a laser induced thermal imaging (hereinafter will be referred to as “LITI”) method. The LITI method may utilize spin coating characteristics as they are, thereby resulting in excellent internal uniformity of pixels in the large-sized OLED. In addition, since the LITI method adopts a dry process instead of a wet process, the LITI method may prevent lifetime reduction by solvent as well as realize a fine pattern in the organic layer.
Application of the LITI method basically needs a light source, an OLED substrate (hereinafter will be referred to as “substrate”) and a donor substrate, wherein the donor substrate includes a base layer, a light-to-heat conversion layer and a transfer layer.
According to the LITI method, light emitted from the light source is absorbed by the light-to-heat conversion layer to convert the light into heat energy, so that an organic material formed on the transfer layer is transferred onto the substrate by the converted heat energy.
Methods of forming a pattern of an OLED using the LITI method are disclosed in Korean Patent Registration No. 10-0342653, and U.S. Pat. Nos. 5,998,085, 6,214,520 and 6,114,085.
FIGS. 1A to 1C are cross-sectional views illustrating processes of patterning an organic layer using an LITI method.
Referring to FIG. 1A, a substrate 10 is prepared, and a donor substrate 20 including a base layer 21, a light-to-heat conversion layer 22, and a transfer layer 23 is laminated on the substrate 10.
Next, as shown in FIG. 1B, a laser X is irradiated on a first region (a) in the base layer 21 of the donor substrate 20. The laser passed from the base layer 21 is converted to heat in the light-to-heat conversion layer 22, and the heat makes an adhesion between the first region (a) and the light-to-heat conversion layer 22 weak.
Continuously, as shown in FIG. 1C, the transfer layer, at which the adhesion is weakened, i.e., the transfer layer corresponding to the first region (a) is transferred onto the substrate 10 to form an organic layer 23a on the substrate 10, and a transfer layer (b), i.e., the transfer layer corresponding to a second region (b) where the laser is not irradiated, is separated together with the donor substrate, thereby forming a patterned organic layer 23a. 
However, in forming the patterned organic layer using the LITI method, static electricity may be generated due to external environmental factors such as friction and so on during attachment and detachment processes of the donor substrate and the substrate. Since discharge voltage of this static electricity has a range of about several thousands to several ten thousands, the static electricity may cause defects such as a short-circuit at adhesion parts, or melting of metal or separation of wiring due to a temperature increase in the device, and therefore device characteristics may be deteriorated due to influence affecting to an inner circuit of the device.